1. Field of the Invention
The present invention relates to a variable focus lens, and more particularly, to a variable focus lens which has a plurality of protrusions formed at one end of a chamber to prevent bubble formation and absorbs volume change of fluid due to changes in external environment such as temperature and pressure to eliminate entry or formation of bubbles, thereby functioning well as a lens regardless of external changes.
2. Description of the Related Art
In general, a camera is equipped with a plurality of lenses and is configured to adjust optical focus distance by driving the lenses respectively to vary the relative distances thereof. Due to the miniaturization of optical devices such as a camera with a lens mounted therein, the miniaturization of the lens is increasingly required in turn.
In order to meet the needs for miniaturization, a variable focus lens has been disclosed in PCT WO 03/069380.
FIG. 1 is a schematic cross-sectional view of the variable focus lens suggested in an embodiment of WO 03/069380.
As shown in FIG. 1, the variable focus lens includes a fluid chamber 5 with a cylindrical wall, containing first fluid A and second fluid B therein which are non-miscible and have different refractive indices. The first and second fluids A and B are in contact over a meniscus 14 in between. The variable focus lens also includes a fluid contact layer 10 disposed on an inner side of the cylindrical wall of the fluid chamber 5, a first electrode 2 separated from the first fluid A and the second fluid B by the fluid contact layer 10 and a second electrode 12 acting on the second fluid B.
The first electrode 2 has a cylindrical shape and is coated by an insulating layer 8 with metallic material. The second electrode 12 is disposed at one end of the fluid chamber 5.
In addition, the fluid chamber 5 is covered by transparent front and back elements 4 and 6 to house the fluids A and B.
In addition, a sealing (shown in FIG. 4 and denoted by reference numeral 16) is provided to bond the front element 4 with the fluid contact layer 10.
The operation of the variable focus lens with the above described configuration is as explained hereunder.
When no voltage is applied between the first electrode 2 and the second electrode 12, the fluid contact layer 10 has a higher wettability with respect to the first fluid A than the second fluid B.
Due to electrowetting, wettability by the second fluid B varies under the application of voltage between the first and second electrodes, which changes the contact angle Q1, Q2 and Q3 of the meniscus 14 as shown.
Therefore, the shape of the meniscus is variable in response to the voltage applied, thereby adjusting the focus of the lens.
That is, as shown in FIGS. 1 to 3, in accordance with the magnitude of the voltage applied, the angle of the meniscus 14 and the fluid contact layer 10 measured in the side of the first fluid B changes from an obtuse angle to an acute angle, for example, in the order of 140°, 100°, 60°, etc.
Herein, FIG. 1 shows a lens configuration with high negative power, FIG. 2 shows a lens configuration with low negative power and FIG. 3 shows a lens configuration with positive power.
The variable focus lens using the fluid as described above has an advantage for miniaturization over the conventional method of adjusting focal distance by mechanically operating the lenses.
However, the conventional variable focus lens has drawbacks as shown in FIG. 4. That is, as the variable focus lens contains fluids, if the fluids are not properly sealed, bubbles 18 may be formed inside the chamber 5 as shown in FIG. 4.
The drawbacks of the conventional variable focus lens will now be explained in greater detail with reference to FIGS. 5 and 6.
First, as shown in FIG. 5, the fluids A and B are filled between the space between the chamber walls 30, forming a convex surface, but not to the degree of flowing over an upper end 32 of the chamber wall. At this state, an upper transparent plate 40 is moved downward in the direction indicated by the arrow C, the fluid A contacts the undersurface of the upper transparent plate 40 and spreads along the undersurface of the upper transparent plate. Thus, when the upper transparent plate 40 is completely attached to the chamber wall 30, a bubble V is formed in the middle of the fluid A as shown in FIG. 6. The fluid lens is not usable if such a bubble is formed. This is an example of the problem described with reference to FIG. 4.
To prevent such a problem, the lens can be assembled inside the liquid, which however does not completely suppress the formation of the bubbles, diminishes productivity and hinders mass production of lens.